George Thomas Clark, Mediæval Military Architecture in England…
“ One lies west and another east of the north gate, and there is a considerable mass south of the north-east angle, capping which, the foundations of a round tower, of 9 feet interior diameter, have been discovered. There is also a fragment of wall in the slope of what is called the observatory mound, a little west of the remains of the south gate. The exterior ditch, also more or less Roman, is in parts very perfect, broad and deep along the north front, and, though narrower, deep and well preserved about the north-east angle. ”
